1. Field of the Invention
The present invention relates to a user equipment (UE), and more particularly, to a user equipment apparatus for transmitting a plurality of signals simultaneously using at least two wireless communication schemes and method thereof.
2. Discussion of the Related Art
Recently, the demand for a use of radio waves keeps increasing owing to the remarkable development of the wireless communication technology. And, the radio waves are widely used for the medical industry, traffic control and daily life as well as for communications and broadcasting fields. Thus, as the use of electric devices rapidly increases, the electromagnetic waves radiating from the radio wave use facilities and devices have considerable influence on human body. Specifically, in case of a mobile communication device, U.S. FCC (Federal Communication Commission) adopts the guideline for environmental influence evaluation on radio frequency radiation of FCC 96-326 to regulate a limit for local power absorption applicable to a random mobile transmitting device. In this case, the limit of maximum allowable exposure is based on the exposure evaluation reference quantified into a specific absorption rate (SAR) that is a measure of a radio frequency (RF) energy absorption rate. In case that electromagnetic waves are applied to a human body, the quantity evaluation on the electromagnetic waves is performed by power measurement, electromagnetic field analysis and SAR measurement through animal tests and the like. In this case, the SAR is represented as absorption power per unit mass, which is absorbed in a human body exposed to an electromagnetic field in general.
CENELEC (Comit'e Europeen de Normalisation Electrotechnique) regulates SAR condition as the requirement for the suitability evaluation on a mobile communication user equipment as well as U.S. FCC. Thus, U.S. FCC, CENELEC and the like specify the SAR condition as an important item for the suitability evaluation on the mobile communication terminal despite differing in a reference value of the SAR condition. Therefore, the mobile communication terminal should meet the SAR condition or rules.
In general, a user equipment in a wireless communication system needs to abide by Specific Absorption Rate (hereinafter abbreviated SAR) rules even if transmitting signals on at least two frequency bands. For this, a user equipment according to a related art measures a power of a first frequency band and a power of a second frequency band and then saves the measured power values. And, the related art user equipment previously determines how much power will be backed off in accordance with the power of each of the two frequency bands. In this case, the value of the power to be backed off in accordance with the power of the corresponding frequency band is previously defined in such a format as a table and the like.
For instance, when a user equipment transmits a signal on a first frequency band with maximum power, a power of a second frequency band different from the first frequency band will apply to a power backoff as much as possible. Likewise, when the user equipment transmits a signal on the second frequency band with maximum power, a power of the first frequency band will apply to a power backoff as much as possible. Moreover, in case that a user equipment transmits a signal on one frequency band not with a maximum power but with a specific power value, a quantity of a power backoff, which will apply to the other frequency band is already determined in advance. In particular, Quantities of the power backoff, which will apply to various power values of a signal transmitted on the first or second frequency band, are defined as a table in advance.
In case of the real implementation of the above power backoff quantity, assuming that a transmission power of a signal transmitted on a specific frequency band is already known, a transmission power of a signal transmitted on another frequency band is measured by real time. And, the power backoff quantity previously defined for each of the two transmission power values is applied.
A power backoff reference applied in this scheme is implemented to apply a specific power back-of quantity to a value in a specific range instead of an absolute value. In case of this implementation, a measured transmission power value belongs to a specific section. If an initial value in a range of the section is compared to a last value in the range of the section, there is a contradiction that a backoff quantity is identical despite a power difference in-between. Hence, this contradiction causes a problem that application of an elaborate and precise power backoff is difficult. Moreover, when a range is determined with a sufficient margin, it causes another problem that an unnecessary power backoff is generated.
Even if a table for the power backoff is prepared in a manner of setting a specific section to a range of a small value to solve these problems, a section, to which a power backoff will be applied, varies despite a small error occurrence in a measurement of a power value in aspect of real implementation. Moreover, it is difficult and inconvenient to measure a power value by a fine unit.
Moreover, a method of measuring a transmission power of a first wireless communication chip and a method of delivering the measured transmission power to a second wireless communication chip have not been proposed in detail so far.
As mentioned in the forgoing description, a user equipment in a wireless communication system needs to abide by the SAR rules in case of transmitting signals, to which at least two different wireless communication schemes are respectively applied, simultaneously. While two wireless communication chips are transmitting signals with maximum power, in order to prevent a case that the SAR reference is exceeded, a power of the signal transmitted by one of the two wireless communication chips should be estimated. Yet, if it is impossible to perform initial transmission power estimation in a situation that open-loop power control is performed like RACH state, it causes a serious problem that the SAR is not met. And, a solution of this problem has not been proposed at all.